bug#30697: make eval-expression only take `read'-able Lisp

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 04 Mar 2018 17:46:18 +0100
> From: charles@aurox.ch (Charles A. Roelli)
> 
> Here is a change to make eval-expression issue a warning in the
> minibuffer when the user enters an unreadable expression.  Currently,
> we just error out, so the user has to restart the command and go back
> in the history to get back what he typed.
> 
> With the change applied, if you type
> 
> M-: ( RET
> 
> from emacs -q, you'll see,
> 
> Eval: ( [End of file during parsing]
> 
> which gives you a chance to fix the error right away.
> 
> As another example, if you type an extra paren, as in
> 
> M-: ( ) ) RET
> 
> you'll see,
> 
> Eval: ()) [Trailing garbage following expression]
> 
> and point is left at the extra paren.

You are changing the behavior of read--expression, which has a few
callers in Emacs.  Did you verify that those callers won't break due
to this change?

This should also have a NEWS entry, and perhaps the manual needs some
changes, please take a look.

Thanks.